Objective-In this study, we characterized the effects of an osteopontin (OPN)-null mutation in normal arterial function and remodeling in a murine model. Methods and Results-OPN-null mutant mice were compared with wild-type mice before and after carotid artery ligation.Before ligation, OPN-null mice had increased heart rate, lower blood pressure, and increased circulating lymphocytes compared with wild-type mice. OPN-null vessels also demonstrated greater compliance accompanied by a loosely organized collagen network. After carotid artery ligation, significant differences were also found in the remodeling response of OPN-null animals. 16,17 and shear stress. 9,18,19 We previously found that inhibiting osteopontin (OPN) function after endothelial denudation led to a significant decrease in the extent of neointimal formation in rats. 20 In this study, the arterial effects resulting from the removal of OPN (product of the spp1 gene) were examined.OPN is a secreted integrin-binding protein that is present in small amounts in uninjured arteries 21 but is abundantly expressed by smooth muscle cells, endothelial cells, 21,22 and activated inflammatory cells [23][24][25] in injured arteries. Abundant OPN expression has also been observed in human atherosclerotic lesions 26 and thoracic aneurysms. 27 The functional significance of this increased vascular expression was suggested by work demonstrating OPN activity as a chemoattractant/adhesive substrate for endothelial cells 28 and vascular smooth muscle cells, 29 an inhibitor of vascular smooth muscle calcification, 30,31 and a chemoattractant/activator of inflammatory cells. 32,33 In vivo studies confirmed these important functions of OPN during tissue remodeling and repair. Chiba et al 34 observed that hematopoietic cell overexpression of OPN resulted in increased atherosclerotic lesion formation. In OPN-null mice, recent data have indicated that the nonredundant functions of OPN in vivo involve widespread participation in tissue remodeling, inflammation, 24,32 tumor progression, 35 and angiogenesis. 36 Defective tissue remodeling on an OPN-null background has been observed in tissues including the myocardium, 37 bone, 36,38 -40 skin, 41 kidney, 42-44 lymph nodes, 45 joints, 46 and malignant tissues. 35 Two phenotypes that characterize many of these studies are a change in the immune response and altered matrix remodeling. Therefore, the widespread participation of OPN in tissue remodeling is likely due to its unique functions in basic repair processes. In addition, the role of OPN as a physiological inhibitor of vascular calcification was demonstrated in studies showing that spontaneous vascular calcification in the matrix of Gla protein-null mice was significantly increased on an OPN-null background. 47 Recently, constitutive overexpression of OPN in mice was observed to result in increased neointima formation after cuffing of the femoral artery. 48 Interestingly, this overexpression of OPN in uninjured mice did not result in accumulation of leukocytes in the vessel...

Ligation of the murine common carotid artery induces a reproducible remodeling response. The contribution of individual genes can be determined by comparison of the phenotypes of genetically modified mice. Although studies have shown the response to carotid artery ligation is influenced by many factors, individual analyses typically only consider a single factor, the presence of a gene of interest. Because of this limitation, measurements of the response to ligation show large variation, making the determination of significant difference between test groups difficult. In this study, we examine the hypothesis that the variation in the response to ligation is due to non-genetic factors in addition to genetic factors. Distance from the ligature, a variable common to all arterial ligation experiments, is an important source of variation and a significant predictor of the remodeling response. We find that the use of statistical regression is an improved analysis technique, as it allows the simultaneous consideration of multiple variables. We demonstrate this by showing improved sensitivity and novel findings in the analysis of the remodeling response in mice genetically mutant for the osteopontin gene. We conclude regression analysis provides a simple way to improve both comparative power and description of vascular remodeling. Chronic obstructive vascular pathology (eg, stenosis, restenosis, arteriosclerosis) remains a widespread health problem and the largest contributor to the morbidity and mortality of both men and women in developed nations. 1 These pathologies each involve a response to a physical stimulus, such as changes in shear stress, direct injury, or oxidative injury, resulting in vascular remodeling and neointima formation. As obstructive pathologies have been shown to involve complex regulation of several cell types, there continues to be great need for in vivo models to understand the mechanistic basis of the pathology.Murine models of vascular disease are especially useful in determining the contribution of specific gene products as genetically modified mice are easily generated and readily available. Current models include mice that spontaneously demonstrate chronic obstructive vascular disease 2 and induction of obstruction by direct injury of the vasculature. [3][4][5][6][7] The complete ligation of the carotid artery is one method of inducing a vascular remodeling response in mice. Originally described by Kumar and Lindner,7 this model has the advantages of being technically simple to perform and yielding a highly reproducible localized vascular remodeling response. This murine model is being increasingly used, and has been instrumental in defining the contributions of plasma protein systems, 3,8,9 cytokines, 10,11 and physical forces such as pressure 12 and shear stress 7 in the vascular remodeling response.Whereas the vascular lesions formed in response to some injuries such as endothelial denudation are relatively consistent over the involved arterial segment, carotid artery ligation induces ...

No abstract